Gas generating cartridge



Jan. 21, 1941. J. M. HoLM Erm.

GAS GENERATING CA-RTRIDGE Filed Jan. 12, 193B m l "-7 f ,7.1542454 A TTORNEY Patented Jan. 2l, 1941 GAS GENERATING CARTRIDGE John Maciie Holm, Pollokshields, Glasgow, and William McEwen, Irvine, Ayrshire, Scotland, assignors to Irmperial Chemical Industries'Limited, a corporation ot Great Britain f Application January 12, 1938, Serial No. 184,700

In Great Britain January 20,' 19

4`Claims. (Cl. 102-12) 5 the kind requiring for their operation the development of high pressures, e. g.' of many hundred pounds per square inch, in a gradual manner. As examples of mechanical devices of this kind may be mentioned: high-pressure liquid-ejectors, 4

engineV starters, lorry-tipping devices, jacks, presses, electrical-switch-gear-operating devices, compressed-gas motors, brakes, and other devices koperated by the motion of pistons.

The burning characteristics of ordinary propellent explosive compositions containing colloided nitrocellulose are such that attempts to employ cartridges of ordinary construction containing charges of this nature for the gradual generation of large pressures have hitherto failed to attain their objects. The rate at which the explosive burns in a confined space increases so rapidly as the pressure develops that the time occupied by the combustion of the whole charge seldom amounts to more than 2 seconds, and is usually a fraction of one second. Furthermore, the ratios of the'maximum pressure to the final pressure developed increases so greatly with rise of loading density that in many cases Vsuch cartridges cannot produce large nal pressures without imparting an undesirable shock to some part of the apparatus.

Our specification Serial No. 59,630 describes and claims composite charges and cartridges which are suitable for generating large pressures over a considerable number of seconds without developing unduly high ratios of maximum to final pressure. The charges or cartridges used according to the said specification include a charge element capable of self-propagating combustion when ignited at substantially atmospheric pressure, and

one or more further charge elements capable of generates a pressure of not more than about 10 atms.

Pending application Serial No. 143,949 also describes a composite charge, for use in cartridges for similar purposes, in which at least one of the charge elements consisting of a-compacted composition containing nitroguanidine. a

Although the composite charges, and cartridges containing them, described in the two latter specifications are completely satisfactory for the purposes described, their production is inconvenient, in that the materials exemplified are hygro- 5 scopic or expensive.

,This inventionhas as an object to provide a substantially ashless charge for cartridges of the type described which shall have none of theabove mentioned disadvantages. A further object is to 10 devise a method of manufacturing such charges.

A further object is to provide a charge of this type which will be easy and economical to manufacture. Further objects will appear hereinafter.

These objects are accomplished by the fcllow- 15 'ing invention. We have now found that cartridges burning gas-generating cartridge or charge com- 30 prises a self-combustible substantially ashless propellent explosive composition in the form of a solid rod which is exposed to ignition at one end y c only, and is protected on its longitudinal surface by tightly wrapping around the rod in overlap- 35 ping fashion a tape or sheet of material, forming in combination withan adhesion-promoting substance a closely adherent shield which prevents the contact of axrie gases with the protected surface of the rod d u'ring the combustion thereof.`

The propellent explosives used are preferably non-solvent propellants, e. g. solventless cordite or other double-base propellants. In some cases rods of propellants whose manufacture has involved the use of a volatile solvent may be em- 45 ployed; but, as the difficulty of producing homogeneous and sumciently solvent-free rods of either single or double-base propellant of this type becomes extreme when the diameter of the rod finally produced exceeds about 1 cm.; and as the 50 practical requirements in respect of gas volume and pressure required for successfully operating devices of the'kind described, in conjunction with the characteristic burning speeds of solid propellent explosives, generally call for the use of rods 65 'the exposed end of the wrapped cylinder.

of greater diameter than 1 om.; in practice a nonsolvent propellant is to be preferred.

The wrapping material may conveniently consist of a fibrous or textilebacking material, e. g. woven tape, paper, or the like, coated and/or impregnated with a cementitious adhesion-promoting material such as a cellulose derivative thermoplastic composition, a resinous composition, a rubber or rubber and oxidised oil composition, or a bituminous composition. The wrapping material may also consist of a homogeneous material such as cellulose acetate, regenerated cellulose, sheet rubber or the like; in which case the adhesion-promoting material may be a volatile solvent for the wrapping material and/or for the propellant itself.

Where the adhesion-promoting composition has a solvent effect on the rod, we prefer to apply a final coat of a varnish material that does not propagate its own combustion so that the shield does not lose its protective effect through impregnation with the propellent composition in solution: i

In al1 cases the completed shield is such that it does not propagate its own combustion.

The means of ignition employed in association with the wrapped cylinder may consist of a percussion cap or an ordinary low-tension or hightension fuzehead, in conjunction with priming means such as a small charge of propellent powder, or quick-match fuze or the like, in contact with the ignition end of the wrapped cylinder..

In addition we may use a pellet or disc of a solid propellent composition as part of the lpriming means in order to ensure energetic ignition of This may be effected by leaving a short length unwrapped at the ignition end of the rod.

The cartridge case may be if desired constructed in relatively weak material such as paper, and the materials used in the manufacture of paper shotgun cartridge cases are suitable for use in carrying out our invention.

In use, the cartridges may be associated with a supporting metallic cage leaving a portion of the cartridge wall unsupported at some desired position, so that a vent for the combustion gases is formed by the rupture of the cartridge wall undenthe pressure produced by the combustion of the initiating means or of the initial portion of the charge. When initiated .by a percussion cap of the usual kind, the cartridges may be arranged to vent near the base; and if initiated by electrical means, they may conveniently be arranged to vent at or near the forward end; in which case the use of a metallic supporting cage is unnecessary.

The use according to the present invention of wrapped cylinders of solid propellent explosive as charges ingas-producing cartridges has the advantage that the burning speed does not vary irregularly and uncontrollably on account of destruction or displacement of the shield in the neighbourhood of the burning portion of the rodso that flame gases penetrate through it or between it and the rod beyondthe point of burning, and thus defeat the purpose for which the shield is employed.

Charges according to our invention may therefore be used without dependence on a tightlyfitting indestructible case as hitherto used; and if desired they may be used satisfactorily without any external protection other than that provided by the wrapping. A

It will be understood that the distal end as Well as the cylindrical surface of the rod must 'ne protected from premature ignition; and where the wrapped cylinder is used in conjunction with a cartridge case, a gas-tight t of the wrapped cylinder in the case may be used to protect the distal end from leakage of flame gases between the wrapping and the case. We prefer, however, to apply a positive protection to the distal end surface so that a tight fit by the wrapped `cartridge in the case is unnecessary.

In the attached drawing, Figures 1 and 2 are diagrammatic views in cross-section of cartridges venting near the base for use with percussion ignition. Figure 3 is a similar view of a cartridge arranged for forward ignition by means of an 'electricalfuzehead The invention is further il-v lustrated in the following examples.

Example 1 .The charged cartridge of this example is illustrated in Figure 1.

An unlined paper cartridge case I having two 8 mm. diameter `venting holes 16 mm. from the metal base 2 is employed. Tlie external and internal diameters of the case correspond to those'of an ordinary 12 bore case, namely 19.9 mm. and 18.6 mm. respectively, but 'the length is somewhat greater. The ignition means are situated at the base of the cartridge and comprise the percussion cap 3, a priming charge 4 of 0.4 gm. Schultze gunpowder and 25 mm. quickmatch 5 and a l gm. disc 6 of non-solvent Ardeer cordite 15.2 mm. in diameter having the composition: nitroglycerine 29%, nitrocellulose 65%, diethyl diphenyl urea 6%. The main charge 'I consists of 37 gm. of non-solvent Ardeer cordite rod of the same composition, 127 mm. long. 15.2 mm. in diameter, tightly wrapped from the ignition end with a 1700 mm. length 8 of adhesive electrical insulating tape 13 mm. wide and weighing 8.85 gm. per metre. A disc 9 of modelling clayA is pressed on to one end of the rod and held in position by the projecting end of the tape. The wrapped rod is inserted into the cartridge case with the exposed end in contact with the Ardeer cordite disc, and the cartridgeis closed with a cardboard disc I and turnover Il.

When associated with a close-fitting cage having venting apertures registering with those of the cartridge case and tested by ignition in a closed vessel of 1050 c. c. capacity, the cartridge develops a maximum pressure of 780 lb. per sq. inch in about 40 seconds; the f'lnal pressure being 680 lb. per sq. inch.

Example 2 The cartridge of this example is illustrated in Figure 2.

An unlined paper cartridge case I having a metal 'base 2 provided with a 0.4 grain percussion cap 3 is employed. The external and internal diameters of the paper case-correspond to those of an ordinary 12-bore case, namely 19.9 mm. and 18.6 mm. respectively, but'the length is somewhat greater. The ignition means comprises the percussion cap, a priming charge 4 of 0.1 gm. Schultze gunpowder, a 150 mm. length of quickmatch and a 5.5 g'm. pellet 6 of non-solvent Ardeer cordite 15.3 mm. in diameter and 20 mm. long; these being loaded at the base of the case. The composition of the Ardeer cordite is: nitroglycerine 38.5%; nitrocellulose 47.5%; moderants 14%. A white rubber disc I2 having an external diameter slightly greater than that of the case and 3 mm. thick is placed-between the igniting means andthe main charge 1,' thisdisc'having centralI perforation 7 mm.- :in diameter. The

-main charge consistsof a rod 120 mm. in length of thev same Ardeer cordite composition weighing 33.5 gm., wrapped inoverlapping 4spiral fashion,

startingv from theignition end, with a 1100 mm.

length! of adhesive electrical insulating tape 13 mm. :Wide and weighing 8.85 gm. per metre. 'I'he 1 remote end of the charge from the igniting means 1l; inchcardboard 'disc I0, secured by the usual type of shotgun cartridge case turnover I i. When tested -in the manner described in Example 1 in a closed vessel of 570 cc. capacity the cartridge develops a maximum pressure of about 1800 lb/sq. in. in a gradual manner in 25seconds, the final pressure being about 1500 lb/sq. in.

Example 3 In example the cartridge case, ignition mea-.ns and white rubber disc are as described above" in Example 2. The main charge consists of a 130mm. lengthv of the same Ardeer cordite as used in Example 2 weighing 36.2 gm. and wrapped with two spiral layers of surgical adhesive'tape, the length employed being 2000 mm. and the width 12.5 mm. This tape weighs 2.1 gm. per metre. One end of the charge is protected vby folding over a prolongation of the spiral wrapping and pressing it against the end surface. The charge is loaded in the case and the 'case closed as described above in Example 2. When tested in the manner described in Example 1 in a closed vessel of 1050 c. c. capacity. a maximum pressure of about 1000 lb./sq. in. is developed by the cartridge in 36 seconds; the iinal pressure being about 900 lb./sq. in.

Example v4 The cartridge case, cap, and white rubber disc in this example are as described in Example 2.

In addition to the percussion cap, the priming means includes 0.4 gm. of Schultze gunpowder, a 150 mm. length of quickmatch, and a 12.5 mm. length of Ardeer cordite 15.2 mm. in diameter and weighing 3.7 gm. This Ardeer cordite has the composition, nitroglycerine 30%; nitrocellulose 64%; and diethyl diphenyl urea 6%. 'I'he main charge consists of 127 mm. of this same Ardeer cordite wrapped round yin spiral fashion with a 500 mm. length of grey adhesive rubber tape, 19.3 mm. wide, 0.8 mm. thick and weighing 27.7 gm. per metre. One end of the'charge is protected byl folding over a prolongation of the spiral wrapping and pressing it against the end surface.' This charge is loaded .and the case closed as described in the previous examples. When tested in the manner described in Example 1 in a closed vessel of 1050 cc. capacity a maximum pressure of about 860 lb./sq. inch is developed in 33 seconds, the final pressure being 700 lbs/sq; in. y

Example 5 l In this example thecartridge case, ignition means and white rubber disc are the same as employed in Example 2. The main charge consists of 76 mm. of the same Ardeer cordite as'emsure being 400 lb.sq. in.

pioyed in Example 2 and weighs 21.2 gm. It is wrapped'in aspiral fashion-with 620 mm. of a maskingpaper tape 25 mm. wide and weighing 4.9 gm. per metre having a coating of a thermoplastic adhesive. One end of the main charge is protected by folding over a prolongation of the 'spiral wrapping and-pressing it against the end surface. vThis charge is loaded and the case closed as described in Example 2. When tested as in Example 1 ina closed vessel of 1260 cc.

capacity the cartridge develops a maximum pressure of about 420 lb./sq..in. in 33 seconds, the

final pressure being about 400 lb./sq. in.

Example 6 a protected rod of Ardeer cordite of a diierent composition, namely that used according to Ex- 'ample 2, the rod being 15.3 mm. in diameter,

76' mm. long and weighing 21 gm. in its un, wrapped state. The rod is protected by dipping it in acetone and winding it tightly with a strip of acetone-soluble cellulose acetate 96 mm. broad and 0.22 mm. thick and somewhat longer than' the rod, the overlap being sealed with the aid of acetone.

One end of the wrapped rod is sealed oil with modelling clay and the rod is inserted with the exposed end in contact with the 4 gm. disc. When tested in the manner described in Example 1 the cartridge produces a. maximum pressure of 425 lb./sq. in. in 321/2 secs., the iinal pres- Example 7 This example describes the cartridge adapted for forward ignition and illustrated in Figure 3.

'Ihe charge consists of a solid homogeneous cylinder 7 of solventless cordite 108 mm. long, 23 mm.- diameter and weighing 67 gm., and consisting. of nitroglycerine 35.5%, nitrocellulose 51%, diethyl-diphenylurea 5%, diamyl phthalate 7% and potassium nitrate 1.5%. A 1400 mmf length of tape 8 which is 13 mmfwide and is impregnated with an adhesive castor-oil rubber composition, is wound tightly round the rod in an overlapping spiral so that 10 mm. at one end of the rod is left uncovered; the other end being y sealed oi by a disc of similar adhesive tape over which the projection portion of the wrapping is turned down. 'I'he wrapped cylinder is inserted, sealed end foremost, intov a paper shotgun cartridge case i which is 26 mm.' in external diameter, 24.5 mm. internal diameter, and 13o mmlong.' The case is tted with a brass shell 2 having an insulated central electrode I4. The means of ignition consists of an ordinary low-tension electric fuzehead I7, whose insulated leads I3 are connected to the brass base and the central electrode respectively and are led forward between the case and the wrapped cylinder so that the fuzehead is in contact with the exposed end of the rod. A 33 mm. length of quickmatch fuze 5 weighing 0.22 gm. and 0.1 gm. of Schultze gunpowder l are also loaded in contact with the exposed end oi the rod, and the case is closed by a Celluloid disc I0, which is 24.5 mm. indlameter and 0.5 mm. thick, and the usual type of shotgun case turnover il lili When the cartridge is loaded directly in the breech of a closed test vessel of about 1330' ml. capacity and the fuzehead iired by the applica- `tion of a suitable firing current, a maximum Example 8 This example illustrates the use of an unenclosed Wrapped charge.

A 280 mm. by 7 mm. diameter rodof solventless cordite weighing 19.3 gm. and consisting of nitroglycerine 41%, nitrocellulose 52% and diethyldiphenylurea 7% is wrapped in a double overlapping spiral of 730 mm. of a textile adhesive tape as described in Example 4. 25 mm. of the rod is left exposed at one end, and the other end is protected by folding over the projecting portion of the adhesive Atape 50 mm. of quickmatch tape 6 mm. wide and a low-.tension electric fuzehead are bound to the exposed end of the rod with cotton thread, and the insulated fuzehead leads are connected to the firing terminals cfa closed testing vessel of 1 litre capacity.

When red inside lthe vessel. the charge produces a very gradual rise of pressure'to a maximum of 800 lb./sq. in. in about '12 seconds; the final pressure being about 750 lb./sq. inch.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof. it is to be understood that we do not limit ourselves to the specic embodiments thereof, except as defined in the appended claims.

We claim:

1. A slow burning gas generating cartridge comprising a solid rod of a self-combustible, substantially ashless propellent explosive composition, and a non-metallic shield covering the longitudinal surface of said rod, said shield being of such composition as to prevent the contact of ame gases with said covered surface during combustion and comprising a layer of non-metallic imperforate sheet material in combination with an adhesion promoting substance disposed in close contact with said rod, and ignition means associated with said cartridge, one end only of said rod beine,r exposed thereto.

2. 'I'he cartridge of claim 1 whereinA the shield comprises -a non-metallic fibrous backing material in combination with an adhesion promoting substance.

3. The cartridge of claim 1 wherein the shield comprises regenerated cellulose in combination with an adhesion promoting material.

4. The cartridge of claim 1 wherein the shield comprises cellulose acetate in combination with an adhesion promoting material.

JOHN MACFIE HOLM. WILLIAM MCEWEN. 

